I am not able to understand the concept of polyatomic ions and valency could you plz explain it in simple terms and how will we know what is the ion charge on an element.

Asked by Harshita Singh | 21st Oct, 2015, 04:26: PM

Expert Answer:

In chemistry, ions can be a single charged atom, or they can be a group of atoms that act as an ion. These groups of atoms are called as polyatomic ions. In polyatomic ions each ion carry a specific charge, which is determined by their numbers of valence electrons.

Step 1

Determine the oxidation number of each atom in the polyatomic ion. For example, consider the hydroxide ion, which has an oxygen atom and a hydrogen atom. The oxidation number of oxygen is -2, and the oxidation number of hydrogen is +1.

Step 2

Add together the oxidation numbers of all the atoms in the polyatomic ion.  In the above example, -2 +1 = -1. This is the charge on the hydroxide ion which is a polyatomic ion.

Step 3

Write this charge as a superscript to the right of the polyatomic ion's formula. For a single charge, write - or + instead of 1- or 1+. In the example, the hydroxide ion is expressed as OH¯.

Answered by Prachi Sawant | 23rd Oct, 2015, 10:27: AM